This invention relates to systems for removing particulate matter suspended in a fluid, and more particularly to systems for removing fine particles from cooling fluid utilized in combination with the machining of metal or non-metals.
There are many applications in which it is necessary for environmental reasons, or for the reclamation and recycling of resources, to separate particulate matter which is suspended in a liquid, from the liquid itself. One example of such an application is the need to remove particulate matter from water used by an industrial floor cleaning machine, or a street sweeping machine, prior to disposing of the water in an environmentally safe manner. Another example of such an application is the removal of waste material from coolant used with cut-off saws or grinding machines. Yet another example of such an application is the necessity to separate chips and fine particles of waste material from coolants used with machine tools to facilitate the machining of metal or non-metallic materials.
The process of machining a workpiece into a finished part on a machine tool requires that a cutter be applied to the workpiece to remove certain material portions of the workpiece in order to achieve the desired shape or finish in the resultant part. The action of the cutter against the workpiece generates a quantity of removed material such as chips or fine particles. The action of the cutter also typically generates a substantial amount of heat in the cutter and in the workpiece. These chips or particles of waste material, and the heat generated, must be removed from the cutter and the workpiece, and must be transported away from the cutter and the workpiece during the machining process, in order to achieve dimensional accuracy of the finished part, and in order to allow the cutter to operate at the high speeds necessary to effectively and efficiently shape the finished part without overheating.
In order to remove the chips or particles, and the heat generated in the machining process, machine tools generally incorporate a cooling and flushing system for directing a flow of a coolant liquid or oil at the workpiece and cutter during the machining process. The coolant liquid or oil absorbs heat generated at the interface of the cutter and the workpiece, and transports heat, chips, and particles away from the cutter and the workpiece. After flowing over the cutter and the workpiece, the coolant fluid, with the chips and/or particles entrained, is collected and removed from the machine tool.
Modern machining processes are carried out at very high speeds, requiring a large flow of coolant fluid for effective removal of the chips and heat. Depending upon the machining process involved, a continuous flow of coolant is required during the machining process at flow rates in the range of 10 to 400 gallons per minute. This flow of coolant is typically supplied to the machine tool by a coolant fluid circulating and cleaning system which includes mechanisms for separating the chips and particles from the flow of coolant so that the coolant can be continuously re-circulated. This invention is directed at novel apparatus and methods for effecting such separation of particulate material from the cooling/flushing fluid.
In conventional cleaning systems, larger sized chips or particles of waste material are separated, from the cooling fluid primarily by the force of gravity. In some coolant cleaning systems which utilize scraper type conveyors, the coolant fluid drained from the machine tool is directed into a dirty fluid reservoir of the coolant cleaning system where the chips and particles are allowed to settle in the bottom of the reservoir. A conveyor mechanism then scrapes across the bottom of the reservoir to pick up the settled chips and particles and transports them to a chip collection bin or container. The coolant which is above the bottom of the tank is then drawn off by a pump and re-circulated to the machine tool. In other coolant cleaning systems, the coolant with entrained chips and particles is directed onto a screen, or a hinge belt conveyor system, as the fluid enters the dirty fluid reservoir, so that the fluid can run through the screen or hinge belt into the bottom of the reservoir, with the larger sized chips and particles being screened out and separated from the coolant fluid by the screen or hinge belt. The liquid and the relatively smaller particles pass through the screen or belt and into the underlying pool of coolant. The particles tend to settle to the bottom of the pool, and are removed by a scraper. The supernatant liquid is collected, and re-circulated to the machine tool. A permanent magnet may be disposed on the bottom wall of the reservoir to supplement the force of gravity with magnetic attraction of ferrous chips and particles in a downward direction toward the bottom wall of the reservoir.
Although known coolant cleaning systems which utilize the force of gravity work reasonably well for larger sized chips and particles, there are several inherent problems involved in the practical application of such systems which have led the designers of such systems to also include additional filtration devices in their systems.
For coolant systems which rely on the force of gravity to cause the chips and particles of waste material to settle out on the bottom of the fluid reservoir, one inherent problem is that the flow rates of coolant demanded by modern machining processes do not allow the fluid to remain stagnant in the fluid reservoir long enough for smaller chips and fine particles of waste material to settle out in the bottom of the tank. While, in theory, and given enough time, all particles of waste material would eventually settle to the bottom of the tank, practical considerations, such as limitations on floor space, prevent system designers from providing fluid reservoirs large enough to enable all particles to settle to the bottom. For example, a coolant system which is required to provide 400 gallons per minute of coolant to a machine tool would need to have a fluid reservoir capable of holding 2000 gallons of incoming dirty coolant in order to allow the coolant to remain in the reservoir for a period of five minutes before being re-circulated to the machine tool. In practice, a reservoir this large simply takes up too much floor space for most applications. As a compromise, the fluid reservoir capacity of many coolant cleaning systems is designed to hold enough coolant for the coolant, on average, to remain in the reservoir for 1 to 1.5 minutes before leaving the reservoir for recirculation. This means that the coolant in the reservoir is never really stagnant, but is actually flowing through the reservoir at a rate high enough to keep some of the finer particles suspended in the fluid. Swirling and churning of the fluid in the tank, caused by draw down of the circulation pump and the actions of conveyors, hinge belts, and the like moving through the reservoir, increase the quantity of relatively finer particles which remain suspended in the coolant.
Even if the coolant in the fluid reservoir could remain relatively stagnant, other factors such as viscosity and surface tension of the coolant tend to cause the relatively finer particles to remain suspended in the fluid rather than to settle out. Given the tight tolerances required in some machining operations, even a small percentage of suspended fine particles is of enough concern to motivate the user to employ additional efforts to remove additional material beyond that which can be removed by the force of gravity.
Coolant cleaning systems which utilize a hinge belt or inlet screen to catch and convey away the chips and particles of waste material as the fluid enters the reservoir, rather than allowing them to settle to the bottom for removal by a conveyor, also must deal with the problem of removing the finer particles which remain suspended in the fluid. All of the factors described above in relation to coolant cleaning systems which rely on settlement of waste material to the bottom of the fluid reservoir, which enable relatively finer particles to remain suspended in the fluid, such as swirling or churning of the fluid, surface tension effects, etc., are also present in cleaning systems which utilize inlet screens or hinge belts to capture the larger chips and particles as the dirty fluid enters the reservoir. For these systems, as a practical matter, the mesh size of the inlet screen or the spaces that allow passage of the fluid through the belt must be large enough to allow the majority of the waste material to be removed at very high rates, given the large volume of waste material which must be dealt with as a result of the high speeds of modern machining operations. Stated another way, floor space considerations place practical limitations on the size and operating capacities of particulate matter removal and conveying devices, resulting in such devices being designed to tolerate the passage of finer suspended particles in order to handle the volume of larger chips and particles in the space available for the inlet screen or conveyor at the prescribed rate.
In the most commonly utilized approach to providing additional filtration of the coolant fluid, a drum filter rotatable about an axis of rotation of the drum is provided. The drum includes a generally cylindrically-shaped screen on the outer periphery of the drum. The drum filter is positioned within the dirty fluid reservoir in such a manner that fluid containing entrained or suspended particles flows into the drum through the cylindrical screen in a direction of flow oriented generally perpendicular to the axis of rotation of the drum. An opening is provided in an end wall of the drum, and a corresponding opening is provided in a wall of the fluid reservoir, so that once the fluid has flowed into the drum through the cylindrical filter in a direction perpendicular the axis of rotation, the cleaned fluid inside the drum can change direction inside the drum and exit through the opening in the end wall of the drum and the corresponding opening in the wall of the fluid reservoir in a direction generally parallel to the axis of rotation of the drum.
A dynamic seal is generally provided in the fluid reservoir between the end wall of the drum and the wall of the fluid reservoir to prevent the dirty fluid from bypassing the drum filter, and to prevent the cleaned fluid, which is exiting the end wall of the drum from re-entering the fluid reservoir. Backwash nozzles for directing a spray of fluid or air either at or outward through the cylindrical screen are also generally provided to remove particulate matter adhering to the outside of the cylindrical screen. Typically the backwash nozzles are located inside the drum. The drum is generally rotated either by a drum sprocket attached to the outer periphery of the drum in such a manner that a portion of a chip conveyor chain or belt moving under or over the outer periphery of the drum engages the sprocket and turns the drum, or the drum is rotated by a separate drive apparatus which separately drives the drum.
It is also known to use multiple drum filters in parallel in a single filtration apparatus, thereby to provide fractional filtration of the dirty coolant so that filtered coolant with varying degrees of cleanliness can be supplied to match the cleanliness requirements of various machining operations.
However, there remains a need for systems, apparatus, and methods of removing the relatively finer particles more efficiently and more effectively.
There remains a need to remove even smaller size particles than are removed according to known art.
There is a need to remove a higher fraction of especially the smaller size particles then are removed according to the known art.